JPS6237392A - Radial cell electroplating apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a radial bath electroplating apparatus.

In particular, the invention relates to an apparatus particularly suitable for high current densities IX of metals and metal alloys, in which the electrolyte flow conditions can be adjusted to optimize the plating process and the quality of the resulting coatings. It is something.

BACKGROUND OF THE INVENTION In the continuous electrodeposition of metals or metal alloys onto metal strips, especially steel strips, high current density processes involving current densities of 50 A/dm'' and above are rapidly evolving. 80 to 12 OA/dm'', but it is expected that significantly higher values will be adopted in the future.

Of course, high deposition rates can be obtained by high current densities, but the electrolyte is applied to the strip to be plated in such a way as to minimize the thickness of the electrolyte layer in contact with the metal strip, which is deficient in metal ions for deposition. It is well known that it is also necessary to have considerable speed. In fact, only in this way can the speed and efficiency of the electroplating process be maintained.

However, in precipitation processes of this type, where high process efficiency and consistently high quality of the products are required, of course together with low production costs, a whole series of operating parameters must be optimized. For example, the constant parallelism between the strip (cathode) and the counter electrode (anode), the voltage drop between the electrodes and along the strip itself, the flow conditions of the electrolyte, the gas at the anode, to name a few of the main ones. There are factors such as the degree of aeration of the electrolytic solution and the current density that are caused by this.

First of all, regarding the clearly important parameters, namely the constant parallelism between the electrodes and the voltage drop, a very useful answer can be obtained by introducing and improving what is known as a radial bath. . In fact, in these devices, a large rotating drum is partially immersed in the electrolyte, and the metal strip to be plated is in close contact with a submerged part of the drum and is moved along with it.

There is an anode at a small distance from the drum surface, and the electrolyte is directed through the space between the drum and the anode, ie, between the strip and the anode. Since the strip is held firmly against the submerged surface of the drum, the problem of maintaining a constant distance between the strip and the anode is solved.

Next, the drum can act as a conductor, or the feed roller can be
Either the strip can be positioned in contact very close to the point where it enters the electrolyte, and in this way the voltage drop problem is also overcome.

However, other problems, particularly those related to electrolyte velocity and aeration, have recently become reasonably recognized, but no satisfactory solution has yet been found.

It has already been established that the quality of the plating, as well as the uniformity of its composition in the case of alloy electrodeposition, depends on the uniformity of the relative velocity of the strip and the electrolyte. It has also recently been recognized that a certain relationship between current density and electrolyte turbulence must be maintained in order to obtain very high quality coatings. See Italian Patent Application No. 411371-A/85).

All these constraints mean that existing documentation and proposals regarding the known art will yield a product of sufficiently high quality to justify the extremely complex nature of the plant and process required, as well as the costs associated therewith. This means that it was completely inadequate to guarantee that.

In fact, in order to obtain a suitable bath length for industrial electroplating, it is necessary to have a drum of very large diameter, for example 2 degrees in diameter, with the result that the circumference of the submerged drum half is The length will be approximately 311 cm, which is not long enough to obtain a regular constant flow of electrolyte into the plating bath (the strip is 1.831 mm wide, and the space between the electrodes is approximately (Please note that the range is from 6-8xm to 2.5-3CIII)
. Moreover, due to the too large length, the gases that inevitably occur at the anode cannot be effectively dispersed.

To overcome these difficulties, the electrolyte is fed to the bottom of the tank housing the drum and is split into two streams that rise over its cylindrical surface in a direction perpendicular to the generatrix of the drum. There is. However, even this device is still not satisfactory, since on one side the electrolyte meets the strip moving in opposite directions, while on the other side they meet moving in the same direction, i.e. at a constant The requirement that the relative speed of

Therefore, a device has been proposed in which a drum is surrounded by a large number of chambers containing an electrolytic solution, and the electrolytic solution is moved from chamber to chamber. Although this setup seems very complex and difficult to balance, it also seems to establish trouble-free operation in either plant.

Proposals have also been made for plants in which one of the two electrolyte streams around the drum is fed from the bottom and the other from the top, so as to obtain the desired uniformity of the relative velocity of the strip and the electrolyte.

However, this solution also does not seem to be a satisfactory solution for a number of reasons, as it requires the use of a drum to supply current to the strip. Alternatively, if the current is supplied through pressure rollers contacting the strip upstream and downstream of the drum, the section where the electrolyte flows from the bottom to the top is located at the point where the current enters the strip, i.e. where the voltage drop is minimal. , it is certain that the maximum evolution of anode gas occurs near the point where the balanced effects of gas concentration and minimum voltage drop mutually compensate. However, in other sections, the opposite hand planting occurs,
There is a maximum gas concentration, ie there is now a maximum voltage drop across the strip. Therefore, it is easy to understand that since the precipitation process in these two sections is taking place under different conditions, the precipitates are also different and there is an overall quality reduction in the finished product.

Secondly, there is the fact that radial bath equipment can only plate one side of the strip, ie the side not in contact with the drum. However, the market is demanding double-sided plating strips of considerable quality. As a result, radial electroplating plants have been constructed in which the strip is rotated 180° and run in the opposite direction from its initial direction through the same group of plating baths or parallel groups of plating baths to plate both sides. . However, this last solution is also economically unsatisfactory, since the second section of the plant is operated only when double-sided strips are required. Moreover, the flow conditions when plating the second side are opposite to those when coating the first side, giving rise to all the already mentioned adverse effects on the quality of the final product.

The possibility of back and forth movement between the strip and the electrolyte as well as the supply of electrical current to the strip to be plated has not been found to be a satisfactory answer to the question of how to maximize the quality of the resulting product. I have mentioned above the possibility of
Given that radial bath electroplating equipment is not currently determined to tolerate inferior and inconsistent product quality, it is clear that this related equipment can be utilized under certain limited process conditions. be.

OBJECTS OF THE INVENTION Accordingly, a particular object of the invention is to provide an apparatus for varying operating conditions.

SUMMARY OF THE INVENTION For this purpose, - other things being equal (and provided that the electrolyte has a certain velocity and the resulting flow is sufficiently turbulent) - optimum quality at high current densities. To achieve a coating of strips and electrolyte.

The structure is essentially based on the observation that there must be a relative velocity between According to the present invention, the solution to
It was suggested.

This concept therefore opens up entirely new prospects for radial bath electroplating plants that can direct the electrolyte flow within the electroplating zone in a direction favorable to establishing the yield as well as the overall efficiency of the plating process. It was decided that it would be done.

Thus, an innovation has been established which consists of special suggestions regarding the arrangement of the means for circulating the electrolyte so that the direction and speed of the electrolyte can be easily controlled.

Therefore, a particular object of the present invention is to provide a rotating drum with a horizontal axis, which draws a strip to be plated in contact with its cylindrical surface, and by means of which said strip serves, in part, as a descending groove from the top to the bottom. Known - 1 Another is known as a rising groove from bottom to top - arranged in pairs facing said cylindrical surface of said drum so as to form with said strip surface two longitudinally running grooves. several sets of electrodes, said electrodes terminating downwardly at some distance and extending from the lower end of said electrode arrangement to permit pumping flow of electrolyte through said descending and ascending grooves; and an electrode terminating in at least one pair of conduits disposed in a radial bath electroplating apparatus, the six pairs of conduits supplying an ejector disposed within each of the conduits and discharging the electrolyte. tubular means are provided through the descending and ascending channels for suction from a tank placed above the channel and in communication with the channel, each of the conduits being operated by the ejector to draw the electrolyte; means for supplying the electrolyte from the conduit through the descending and ascending channels in a direction opposite to the direction of pumping it into the tank, and wherein the electrolyte flow in the descending and descending channels is A radial bath electroplating apparatus, characterized in that it terminates in cooperating means for establishing in a defined direction and at a desired speed.

Each ejector of said pair is supplied by the same dispenser through a three-way valve so that one or both or both ejectors may be dispensed, or both ejectors may not be dispensed. preferable.

In order to adjust the direction and speed of the electrolyte flow in both the ascending and descending channels independently of each other and to adapt the practical process conditions, suitable means consisting essentially of three-way valves and the necessary means for adjusting the flow of the pump;
It is equipped with a flow control valve. Preferably, said conduit is interconnected by a three-way valve downstream of said ejector and a pipe connecting said three-way valve, said pipe also having a possible bypass function for the three-way valve feeding the ejector. have.

Embodiments of the Invention The present invention will now be described in detail through two possible embodiments shown in FIGS. It is not intended to limit the scope of the claims.

In FIG. 1, the drum 1 rotating around the sleeve is pulling the strip 2 so that the strip 2 follows the path down the groove 6 between the anode 4 and the drum l and then between the anode 3 and the drum 1. It is moving in the direction of the arrow, following the upward path of groove 5. The power feeding rollers are designated by numerals 41 and 42. The electrodes 3 and 4 are connected at the bottom to conduits 8 and 9, respectively, and at the top to a separating baffle which defines liquid receiving areas 23 and 26 for the electrolyte arriving via conduits 35 and 36. Connected to tanks 22 and 25 with overflow plates 38 and 39. Turbulent flow in the liquid receiving areas 23 and 26 and scattering from the areas are caused by the blank plates 24 and 27.
It is blocked by.

According to the illustrated flowchart, the upper tanks 2 are in communication with each other.
2 and 25 are filled by a pump 29 which pumps fresh electrolyte from the tank 28 via the T-tube 40, the control valve 43 and the pipe 35. In this method, groove 5
is also filled with electrolyte. The pump 30 also pumps new electrolyte from the tank 28 through the pipe 13 to the three-way valve 12.
It is being sent to The three-way valve 12, in the position shown, supplies fluid to the ejector 10, which in turn supplies the conduit 8.
Through this, fresh electrolyte is sucked in from the liquid receiving area 23 through the groove 5. When the valve 14 is in the position shown, the primary liquid of the ejector 10 is ejected via the conduit 16 and its secondary liquid is sucked in via the conduit 8.

In this mode, the right side of the device, ie the part of the lifting groove 5, is energized and active.

The left side of the device, ie the part of the lowering channel 6, is then brought into active operation in the following manner.

The electrolytic solution delivered by the pump 29 reaches the T-tube 40, a part of which is sent to the pipe 19 (the flow is regulated by the control valve 44), and further passes through this pipe I9 to the three-way valve 32. sent to. In the illustrated position, the three-way valve 32 sends the electrolyte into the conduit 9 through the pipe 34 and the three-way valve 15 in a direction opposite to the direction of operation of the ejector 11, from which the electrolyte flows into the channel. 6 and the liquid receiving area 26 and drains therefrom by the overflow plate 39;
It is then delivered to a tank 28 via a conduit 20.

In practice, the tank 28 not only stores the electrolyte returned from the electroplating bath, but also purifies it.
Note that it consists of a series of tanks and devices for removing the gases necessarily occurring at the anodes 3 and 4, for example, and for restoring the optimum composition and pH of the electrolyte.

FIG. 1 of the accompanying drawings relates to a flow diagram of the electrolyte and the plating strip (running in countercurrent flow to each other).

However, it will be readily appreciated that by suitably varying the settings of valves 12.14.15.31 and 32, desired electrolyte flow conditions may be established in grooves 5 and 6.

Thus, for example, if it is necessary to obtain a double-sided plated product, the strip should be rotated through 180° by suitable equipment.
All you have to do is rotate it and pass it through the plating bath in the opposite direction to that described so far, that is, in this case, the only thing you need to do is reverse the settings of valves 12, 14, 15, 31 and 32, and completely The only thing to do is to maintain a steady countercurrent flow.

However, the above description does not exhaust the possibilities proposed by the invention for satisfying self-evident process requirements and/or product quality requirements.

In fact, it has already been mentioned that in order to obtain coatings of good quality, a certain relationship must be maintained between the fluid flow conditions (turbulence) and the current density used.

The optimum relative velocity between the electrolyte and the strip is 2 m/s if the circulation is mostly countercurrent, since it is necessary for the electrolyte to have a certain velocity, depending on the current used. Assuming the density and overall characteristics of the device are as expected, the maximum allowable stripping speed is relatively low, about 1.5 m/s. However, under such conditions, the electrolyte velocity does not allow sufficient dilution of the gas produced at the anode, so the process efficiency will be reduced, as will the product quality. In this case (FIG. 2), in the descending groove 6, the circulation of the electrolyte is in the same direction as the strip 2, but at a high enough velocity to maintain the absolute desired relative velocity value. It is sufficient that it must be.

In the case of the arrangement shown in FIG. 2, the three-way system is arranged so that the fluid pumped by the pump 30 is supplied via the valve 12 to both ejectors lO and 11, and the electrolyte coming from the tanks 22 and 25 is sucked in through the conduits 8 and 9. Valve 12.14.1
The operation is performed by selecting settings 5.31 and 32. In the illustrated device, three-way valves 31 and 32 are configured to allow electrolyte to be supplied directly to tanks 22 and 25 via pump 29.

As you can see, this arrangement allows the establishment of differentially focused flow of the electrolyte.

However, in modern electroplating plants it is common practice to employ strip speeds of 2178 or higher, so within these conditions, including the above-mentioned relative speeds between the strip and the electrolyte, as much as possible Obtaining the best quality product +1 is obviously not something that can be done at all.

In such cases, it may be sufficient to deliver the electrolyte to both grooves in the same direction as the strip at a sufficiently high velocity to maintain the desired relative velocity.

Other possible devices include devices that provide differential diffusion flow. That is, in this case the electrolyte is delivered into both conduits 8 and 9 in a direction opposite to the direction in which ejectors IO and 11 operate.

It is therefore clear that according to the invention, the highest quality product can be obtained for all desired or required electrolytes by simply changing the settings of a few three-way valves.

Finally, there are still other ways to utilize the invention.

Removing a large number of plating baths without removing the line coating is difficult while maintaining the proper position of the coiler equipment, given the need to produce very thin coatings with the associated equipment. Only one ejector, e.g. 10, is utilized to close the shut-off valve 37 and to close the valves 15 and 15 so that the electrolyte coming from conduit 8 rises directly up conduit 9 through pipes 16 and 17. 14 to reduce the current density and therefore the flow rate of the electrolyte in the plating bath.

The final point to note is the function of part 7.
This part 7 forms a separating space between grooves 5 and 6. The surface of component 7 facing the drum is connected to electrode 3
and 4 are closer to the drum than the surfaces of 4 and 4. This surface is also very rough so as to significantly increase the pressure drop of fluid leaking from the high pressure conduit to the low pressure conduit.

With this method, a leakage flow rate equal to less than 20% of the flow rate in the higher pressure branch has been recorded.

Although the invention has been described with reference to several embodiments, those skilled in the art will appreciate that changes and improvements can be made without departing from the scope of the invention as described herein. will be done.

Effects of the Invention The radial WI electroplating apparatus of the present invention has an ejector inside the radial tank apparatus in which a rising groove and an effect groove are formed between a rotating drum and a pair of electrodes in which an electrolytic solution is pumped and distributed. The structure includes an electrolyte circulation means that connects both grooves with a pair of conduits and interconnects the conduits with a three-way valve and a pipe. It is an excellent electroplating system that can be easily controlled by simply changing the settings, resulting in high current density, high quality coatings, and economical plating even when plating on both sides. be.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing one embodiment of a radial bath electroplating apparatus according to the present invention. FIG. 2 is a schematic diagram showing another embodiment of a radial bath electroplating apparatus according to the present invention.

Claims (1)

[Scope of Claims] 1. A rotating drum with a horizontal axis, which pulls a strip to be plated in contact with its cylindrical surface, and by said strip, one from the top to the bottom and the other from the bottom to the top. a number facing said cylindrical surface of said drum and arranged in pairs so as to form with said strip surface two longitudinal grooves, the former known as descending grooves and the latter known as ascending grooves; a set of electrodes, the electrodes terminating downwardly at some distance;
a radial bath electroplating apparatus comprising: an electrode terminating in at least a pair of conduits disposed at a lower end of the electrode arrangement to permit flow of electrolyte under pressure through the descending and ascending grooves; Each pair of said conduits feeds an ejector disposed within each of said conduits and draws said electrolyte through said descending and ascending grooves from a tank located above said groove and communicating with said groove. each of said conduits having tubular means for discharging said electrolyte in a direction opposite to the direction in which said ejector is actuated to pump said electrolyte from said conduit through said descending and ascending channels into said tank. and terminating in cooperating means for establishing that said electrolyte flow in said ascending and descending channels is in a defined direction and at a desired velocity. A radial tank electroplating device characterized by: 2. The radial tank electroplating apparatus according to claim 1, wherein the ejectors of each pair are supplied with liquid by the same liquid supply device through a three-way valve. 3. The conduits are interconnected by a three-way valve located downstream of the ejector and by a pipe connecting the three-way valve, and the pipe is as close as possible to the three-way valve supplying the ejector. Claims 1 and 2 are characterized in that they also have a bypass function.
Radial bath electroplating equipment as described in Section 1.